This invention relates to tagging of objects to be identified and, more particularly, to tagging particles which are easily detected by luminescent response, or magnetic pickup, or both.
In U.S. Pat. No. 3,772,099, dated Nov. 13, 1973, to Frederick M. Ryan, one of the present co-inventors, and Robert C. Miller, is described a fluorescent tagging means for pre-detonation or post-detonation identification of explosives. This is accomplished by a combination comprising spotting phosphor which is excitable by ultraviolet radiations to provide a band-type emission and coding phosphors which emit a line-type emission. All of the phosphors have very small particle sizes and are incorporated into phosphor grains held together by an inorganic cement or a binder and the resulting conglomerate grains are dispersed in the explosive. After an explosion, the phosphor grains can be readily located by the ultraviolet response of the spotting phosphor, and information disclosed by the presence (or absence) of the coding phosphor can then be decoded. The spotting phosphor will also normally provide some additional indicia of information. Further refinements of this tagging system are disclosed in U.S. Pat. No. 3,967,990 dated July 6, 1976 issued to Ryan et al.
To inhibit any tendency for the phosphor conglomerate particles to sensitize the explosives, the individual particles can be encapsulated in an organic plastic material such as polyethylene and a method for so encapsulating these particles is disclosed in U.S. Pat. No. 3,961,106 dated June 1, 1976 to Heytmeijer et al. These encapsulated particles can incorporate an anti-static coating, such as amorphous carbon, in order to prevent electrostatic charging thereof and such a coating is described in U.S. Pat. No. 3,993,838 dated Nov. 23, 1976 to Heytmeijer et al.
U.S. Pat. No. 3,897,284 dated July 29, 1975 to Livesay discloses microparticles for tagging of explosives, which particles incorporate a substantial proportion of magnetite which enables the particles to be located by means of magnetic pickup. Ferrite has also been used. More recently, the assignee of the foregoing Livesay patent has developed modified tagging particles which comprise strips of color coding material having a layer of magnetite affixed to one side thereof and layers of fluorescent material affixed to both exterior sides thereof, so that location of the taggant can be accomplished by visual detection of the luminescent response, or magnetic pickup, or by both. Both the ferrite and the magnetite materials are dark colored, however, and absorptive of both the radiations which excite the luminescent material and the resulting luminescence emitted therefrom, thereby making the particles somewhat more difficult to locate after an explosion.